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The simultaneous control of diesel engine particulate and NOx emissions was targeted in this study. Particulate control was achieved with a trap that incorporated a high-filtration efficiency ceramic honeycomb monolith. Aerodynamic regeneration was used to periodically backflush the monolith filter. Soot was collected in a metallic chamber and was either incinerated by an electric burner or removed by a vacuum cleaner. NOx emissions were reduced by recirculation of filtered exhaust gases (EGR), which was made possible by the high collection efficiency of the employed monoliths. Tests were conducted on the road, driving a diesel vehicle under various loads and speeds. The levels of NO, CO and O2 at the exhaust were continuously monitored using a portable instrument. The particulate filtration efficiency was in the vicinity of 99% using CeraMem and 97-98% using Panasonic traps, respectively, hence the EGR line was effectively particulate-free.

The development of a soot incinerator with dual ceramic filters and an electric strip heater is discussed herein. The incinerator is designed to operate in series with a diesel particulate trap developed previously (1).1 The particulate trap consists of a primary ceramic monolith which serves as the filtering device. Once the primary monolith has collected enough soot from the exhaust flow to induce a substantial amount of back pressure to the engine, it is cleaned aerodynamically using short pulses of compressed air. The soot is then forced through a reed valve and into the incinerator chamber, where some of the particulates come in contact with an electric strip heater and burn. The regeneration air exits the incinerator through two secondary ceramic wall-flow rectangular filters, where any unburned particulates are retained. Filtered regeneration air is, thus, released to the atmosphere.

A novel high-efficiency Pallflex filter has been developed for diesel exhaust after-treatment. The filter media is made of high-melting point boro-silicate glass fibers bonded together to form a paper-like pad that can withstand elevated thermal regeneration temperatures. Each filter element is placed between two fine stainless steel wire meshes, which impart structural rigidity to the fiber matrix and prevent its disintegration. An array of these filter pads, placed 1 cm, apart, is assembled together in an insulated housing. The filters are separated by spacers, which are perforated on one side and plugged on the other side to force the exhaust to flow through the filter elements. Such a trap of a total filter surface area of 1.2 m2 and a volume of 14 liters was tested in the laboratory and on the road to determine its filtration efficiency, back pressure characteristics and regenerability.

Self-cleaning trap configurations have been developed and evaluated for removing particulate emissions from diesel engine exhaust streams. The main feature of this approach is that the traps are being cleaned continuously using compressed air, and thus, do not require thermal or catalytic regeneration to remove the collected particles. The results of this study indicate that the present system, employing ceramic wall flow monolith filters, performs well in simultaneously filtering the exhaust and removing the captured particles from the filter element into a fabric bag. Successful cleaning of the trap was evidenced by a quasi-steady state behavior of the exhaust back pressure that was reached in a fairly short period of time.